1. Field of the Invention
The invention pertains to the field of keratoplasty and, more particularly, to thermokeratoplasty and the application of coolant to the eye during thermokeratoplasty.
2. Description of Related Art
A variety of eye disorders, such as myopia, keratoconus, and hyperopia, involve abnormal shaping of the cornea. Keratoplasty reshapes the cornea to correct such disorders. For example, with myopia, the shape of the cornea causes the refractive power of an eye to be too great and images to be focused in front of the retina. Flattening aspects of the cornea's shape through keratoplasty decreases the refractive power of an eye with myopia and causes the image to be properly focused at the retina.
Invasive surgical procedures, such as laser-assisted in-situ keratomileusis (LASIK), may be employed to reshape the cornea. However, such surgical procedures typically require a healing period after surgery. Furthermore, such surgical procedures may involve complications, such as dry eye syndrome caused by the severing of corneal nerves.
Thermokeratoplasty, on the other hand, is a noninvasive procedure that may be used to correct the vision of persons who have disorders associated with abnormal shaping of the cornea, such as myopia, keratoconus, and hyperopia. Thermokeratoplasty may be performed by applying electrical energy in the microwave or radio frequency (RF) band. In particular, microwave thermokeratoplasty may employ a near field microwave applicator to apply energy to the cornea and raise the corneal temperature. At about 60° C., the collagen fibers in the cornea shrink. The onset of shrinkage is rapid, and stresses resulting from this shrinkage reshape the corneal surface. Thus, application of heat energy in circular or ring-shaped patterns around the pupil may cause aspects of the cornea to flatten and improve vision in the eye. However, devices for thermokeratoplasty generally apply energy through the corneal surface to heat the underlying collagen fibers. Therefore, the maximum temperature can occur at the corneal surface, resulting in possible heat-related injury and damage to the outer layer, known as the epithelium, at the corneal surface. Moreover, devices for thermokeratoplasty may provide inadequate approaches for controlling the depth of heating below the corneal surface and promoting sufficient heating of the targeted collagen fibers while minimizing the application of heat to areas outside the targeted collagen fibers.